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* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

Heating Rates for Protons and Electrons in Polar Coronal Holes: Empirical Constraints from the Ultraviolet Coronagraph Spectrometer  

Steven R. Cranmer   Submitted: 2020-07-31 09:56

Ultraviolet spectroscopy of the extended solar corona is a powerful tool for measuring the properties of protons, electrons, and heavy ions in the accelerating solar wind. The large coronal holes that expand up from the north and south poles at solar minimum are low-density collisionless regions in which it is possible to detect departures from one-fluid thermal equilibrium. An accurate characterization of these departures is helpful in identifying the kinetic processes ultimately responsible for coronal heating. In this paper, Ultraviolet Coronagraph Spectrometer (UVCS) measurements of the H I Lyman α line are analyzed to constrain values for the solar wind speed, electron density, electron temperature, proton temperature (parallel and perpendicular to the magnetic field) and Alfvén-wave amplitude. The analysis procedure involves creating a large randomized ensemble of empirical models, simulating their Lyman α profiles, and building posterior probability distributions for only the models that agree with the UVCS data. The resulting temperatures do not exhibit a great deal of radial variation between heliocentric distances of 1.4 and 4 solar radii. Typical values for the electron, parallel proton, and perpendicular proton temperatures are 1.2, 1.8, and 1.9 MK, respectively. Resulting values for the "nonthermal" Alfvén wave amplitude show evidence for weak dissipation, with a total energy-loss rate that agrees well with an independently derived total heating rate for the protons and electrons. The moderate Alfvén-wave amplitudes appear to resolve some tension in the literature between competing claims of both higher (undamped) and lower (heavily damped) values.

Authors: S. R. Cranmer
Projects: Other

Publication Status: Accepted for publication in ApJ.
Last Modified: 2020-08-03 19:21
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The Coronal Physics Investigator (CPI) Experiment for ISS: A New Vision for Understanding Solar Wind Acceleration  

Steven R. Cranmer   Submitted: 2011-04-20 06:34

In February 2011 we proposed a NASA Explorer Mission of Opportunity programto develop and operate a large-aperture ultraviolet coronagraph spectrometercalled the Coronal Physics Investigator (CPI) as an attached InternationalSpace Station (ISS) payload. The primary goal of this program is to identifyand characterize the physical processes that heat and accelerate the primaryand secondary components of the fast and slow solar wind. In addition, CPI canmake key measurements needed to understand CMEs. UVCS/SOHO allowed us toidentify what additional measurements need to be made to answer the fundamentalquestions about how solar wind streams are produced, and CPI's next-generationcapabilities were designed specifically to make those measurements. Compared toprevious instruments, CPI provides unprecedented sensitivity, a wavelengthrange extending from 25.7 to 126 nm, higher temporal resolution, and thecapability to measure line profiles of He II, N V, Ne VII, Ne VIII, Si VIII, SIX, Ar VIII, Ca IX, and Fe X, never before seen in coronal holes above 1.3solar radii. CPI will constrain the properties and effects of coronal MHD wavesby (1) observing many ions over a large range of charge and mass, (2) providingsimultaneous measurements of proton and electron temperatures to probeturbulent dissipation mechanisms, and (3) measuring amplitudes of low-frequencycompressive fluctuations. CPI is an internally occulted ultraviolet coronagraphthat provides the required high sensitivity without the need for a deployableboom, and with all technically mature hardware including an ICCD detector. Ahighly experienced Explorer and ISS contractor, L-3 Com Integrated OpticalSystems and Com Systems East, will provide the tracking and pointing system aswell as the instrument, and the integration to the ISS.

Authors: J. L. Kohl, S. R. Cranmer, J. C. Raymond, T. J. Norton, P. J. Cucchiaro, D. B. Reisenfeld, P. H. Janzen, B. D. G. Chandran, T. G. Forbes, P. A. Isenberg, A. V. Panasyuk, A. A. van Ballegooijen
Projects: None

Publication Status: White paper describing a proposed NASA mission of opportunity for ISS
Last Modified: 2011-04-20 13:55
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Heating Rates for Protons and Electrons in Polar Coronal Holes: Empirical Constraints from the Ultraviolet Coronagraph Spectrometer
The Coronal Physics Investigator (CPI) Experiment for ISS: A New Vision for Understanding Solar Wind Acceleration

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